Arylmethane dye azides and method of forming colored indicia therewith



United States Patent Ofitice 3,377,185 Patented Apr. 9, 1968 The purpose of this invention is to provide a new series of arylmethane dye salts for use in business recording operations. Another purpose of this invention is to provide a recording system which depends for its action upon the equilibrium between a colored and a colorless azide dye salt. In particular, it has been found that the hydrazoic acid salts of intensely colored cations from diarylmethane and tria-rylmethane dye bases characterized by a logarithmic dissociation constant below 7 may exist in two forms: (1) an intensely colored dissociated form and (2) a substantially colorless associated form depending upon environmental conditions (solvent, temperature, etc.) which prevail.

This equilibrium has been admirably adapted to the preparation of nonstaining nonaqueous recording solutions for use in marking fluids, spirit duplicating, and as a recording media for nonstaining copy papers. This application is a continuation in part of my copending application Ser. No. 200,052, filed on June 5, 1962, for Associated Dye Salts and Method of Forming Colored Indicia Therewith, now U.S. Patent No. 3,193,404.

Previous workers in the field of colorless or nonstaining recording systems have always utilized chemical reactions between two active chemical co-mponents to obtain colored characters. For example, earlier workers, such as Groak, used metathetical ionic reactions between colorless cations and anions to form colored compounds, such as iron gallate. These reactions required moist conditions, and coatings containing such hygroscopic reagents were subject to premature rupture and discoloration. More recent workers, such as Davis and Thacker, have used nonaqueous systems for their reactions, such as the formation of a colored salt from a colorless base and a strong acid. All of these systems are chemical in nature and possess certain inherent defects in their actual commercial application.

Inasmuch as the major objection to the use of triarylmethane dye solutions in recording systems (marking fluids, typewriter ribbons, copy papers, etc.) is due to the ability of these dyes to stain skin and clothing an intense color, what has long been desired is an intensely colored dye salt which will not color ordinary surfaces but will give an intense character only on a desired surface.

The author of the present invention has found that the hydrazoic acid salts of diarylmethane and triarylmethane color bases characterized by a logarithmic dis sociation constant below 7 may exist completely in the colored dissociated form, completely in the substantially colorless associated form, or in equilibrium between the two forms depending upon the ionization power of their environment.

In particular, it has been found that upon exposure to heat or upon contact with highly ionizing reagents or solids such as unfired kaolin, bentonite, and similar surfaces characterized by a high permanent electric dipole moment, the colorless associated form dissociates into ions, one of which is intensely colored, which dissociation can be used for the recording of data and for duplicating purposes. H

It appears that the equilibrium exists between the forms:

which may be Written in the form of Kekule bonds as:

in which the quanticule (c5) of the azide ion contributes to the screening of the central carbon core only under low energy conditions; but upon exposure to higher energy, ionizing conditions, the central core is now adequately screened by only three substituents, and the molecule ionizes.

The particular stability of crystal violet cyanide apparently is due to the fact that the electrically unbalanced cyanide ion effectively distorts the crystal violet ion so that maximum screening of the central core is achieved. So strongly screened is the central core in crystal violet cyanide that dissociation occurs only under the highenergy conditions existing in the far ultra-violet region; and crystal violet cyanide cannot be dissociated by heat or chemical action alone (lead peroxide, for example, will not oxidize it to crystal violet dye). Only in alcohol SOlLlLlOl'lS (and in similar ionizing solvents) exposed to extremely high-energy ionizing radiation will the molecule. ionize. This is not remarkable; for in the high-energy spectral region even oxygen dissociates to form ozone.

The dye salts of the present invention are chosen so that an essentially unsaturated core is completely screened by other groups only at low energy (normal) conditions. Upon exposure to a high-energy environment, the core is then adequately screened by fewer groups; and the molecule dissociates into ions, at least one of which is colored. The dye salt to be used for a given application becomes a matter of determining the screening characteristics of the ions used. Previous experience in this area before the work of the author of the present invention is extremely limited. Many chemists assume that all or anic azides are dangerously explosive; yet the author of the present invention has found certain organic azides (which are ionic in character but are not ionized) to be quite stable. Michlers hydrol azide (4,4'- bis(dimethylamino (benzhydryl azide), for example, melts at C. and begins to decompose slowly at -220 C., resembling ionic sodium azide in this respect. No explosion has ever been obtained under normal working conditions with this compound, which is very soluble in toluene, di'butyl phthalate, and similar solvents.

From the viewpoint of classic theory, these salts are for the most part the salts of weak bases with a moderately strong acid. It is axiomatic in chemistry that the salts of Strong bases-strong acids (sodium chloride, crystal violet chloride, etc.) are always one hundred percent dissociated; but the salts of weak acids-strong bases and of weak bases-strong acids may be more or less associated depending upon environmental conditions. It would 'appear that one method of adapting other dye bases for use in the present invention would be to lower their base strength by suitable substitution. This is achieved in quanticule-donating systems by incorporating quanticuleattracting groups (nitro, trifiuorornethyl, etc.) into the aryl group.

It was found that crystal violet dye, for example, could be nitrated to give 2,2-dinitro-4,4,4"-tris(dimethylamino)triphenylcarbinol (dinitro crystal violet base), a weak base. This weak base can form undissociated dye salts with suitable anions as well as dissociated dye salts with other anions; with the azide ion it forms the associated dinitro crystal violet azide. Similarly, other nitrated triarylmethane dye derivatives are easily prepared for use in the present invention.

Although the associated azide salts of nitrated triarylmethane dye bases are not completely colorless, being a light orange in color, transfer sheets containing these salts are the same yellow color as standard yellow commercial papers and may be substituted into any form where a pale-colored base web is not objectionable. The use of other meta-directing groups than the nitro group to reduce the base strength of triarylmethane dyes, such as trifluoromethyl and N,N-dialkylsulfonamido, will also furnish intermediates for the dye salts of the present invention. In these cases the parent carbinol bases are substantially colorless as are the resultant salts.

The azide salts of the present invention are waterinsoluble. Inasmuch as water is ionizing in nature, colorless solutions of these associated azide salts in acetone or methanol become colored upon addition of water; for this reason the associated salts of the present invention should be used in systems which do not have an appreciable water content.

The author has found that certain unfired silicates such as diatomaceous earth, kaolin, and bentonite possess high ionizing properties apart from their acid-base and oxidation-reduction properties. A clay molecule may be pictured as a large molecule of polymerized silica containing calcium, iron, and other cations. The iron silicate structure gives oxidizing properties to the clay and the calcium silicate gives acidic and ion-exchange properties to the clay, but it is the polymerized silica structure which gives a high electric dipole moment over the surface of the clay. This dipole is stable until the clay is calcined at high temperature, at which point the electric dipole moment disappears; and the aforementioned clays lose their high ionizing properties.

Although other workers in the recording field, notably Bjorksten, Green, and Bour have utilized certain silicates in recording papers, no worker has until now utilized the clays as other than chemical reagents. It is the purpose of this application to describe a practical utilization of the ionizing properties of silicates possessed of a high electric dipole moment.

The compounds of the present invention offer certain advantages over the color bases from which they are derived. As the method of color formation by dissociation r is different from the method of color formation by reaction of a dye base with an acid, there is oftentimes a marked increase in the rate of reaction. Dinitro crystal violet base, for example, when pure, forms a colored salt with acid silicates only very slowly (3-5 minutes for full color development); but the dissociation of dinitro crys tal violet azide to the colored ion under the influence of the silicates electric dipole moment is immediate, and the intense colored print appears immediately upon recording with this azide salt. The associated azide salts formed can be more readily handled without chemical staining than can the more reactive color bases. The azide salts as a class have good solubility in lipophilic recording fluids. While the compounds of the present invention cannot be used in aqueous solutions, they do, however, have applications in recording systems where a nonvolatile colorformer is desired which will record colored indicia on selected areas from a low-cost lipophilic solvent.

DESCRIPTION Michlers hydrol (4,4'-bis(dimethylamino)benzhydrol) 2,2 dichloro-4,4'-bis(dimethylamino)benzhydrol, ethyl hydrol (4,4-bis(diethylamino)benzhydrol), dinitro crystal violet base, and other compounds of this type are dissolved in glacial acetic acid to form the intensely colored acetate. To this cooled solution is added an aqueous solution of sodium azide (the sodium salt is preferred but other alkali-metal salts of hydrazoic acid or hydrazoic acid itself can be used) until the intense color becomes a markedly lighter color. The axide salt may be deposited at this time or it may be retained in solution. Ice water is added then cold ammonium hydroxide solution is added to precipitate out the Water-insoluble azide. The precipitate is collected washed with water, dried and recrystallized from ethanol or benzene-petroleum ether to give the azide -salt.

The reaction may be carried out in dilute aqueous acids or in acidic alcohol. All that is necessary is that the dye base should be converted to the colored salt before adding the azide ion. The yield of colorless azide dye salt is usually above ninety per cent. Although the associated sulfinate dye salts disclosed in my copending application, Associated Dye Salts and Method of Forming Colored Indicia Therewith, are nontoxic; the azide salts of the present invention are somewhat toxic, especially when ingested. While their solutions can be handled without toxic symptoms, the azide salts of the present invention cannot be given internally as can the chloride, sulfate and other salts of arylmethane dyes.

The azide salts of the present invention are more susccptible to photochemical decomposition than the sulfinates, and the colored forms are not as light-stable as the colored forms of the sulfinate salts. The azide salts do possess unexpectedly good solubility in non-polar organic solvents such as toluene, turpentine, and paraffin oil as well as in nonionizing solvents such as dioctyl phthalate. The azide salts tend to dissociate more readily than the sulfinate salts, and they are not as versatile in their commercial applications as the sulfinate salts. The major attraction of the azide salts is in those applications where solvent cost is important; for example, paraflin oil costs approximately 3-4/pound where dioctyl phthalate costs 15 pound. Where light-stability and certain other factors are not critical, the azide salts of the present invention furnish colorless recording fluids from low-cost solvents and solvent mixtures.

Color is developed in the associated azide dye salts after they have been placed or transferred to a receiving sheet, as imprinted indicia, by exposing said receiving sheet to a highly ionizing environment. Three highly ionizing environments are particularly useful for this purpose. These are a polarizing reagent, a high temperature, and a surface carrying a high permanent electric dipole moment. For example, if a recording fluid comprising an azide salt and a solvent therefor is used to imprint indicia on an ordinary paper, after the solvent has evaporated, color is imparted to the dye salt by exposing the paper either to an elevated temperature or to a polarizing reagent, such as water, ammonium persulfate solution, etc. In other words, color is imparted to the dye salt either by heating the imprinted dye salt .or an imprinted dispersion thereof in a nonvolatile vehicle, or alternatively by treating the paper with a polar developing fluid. The developing fluids preferably contain water, but water alone cannot be used by itself because the azide dye salts are insoluble therein. It is necessary, therefore, in the case of water as a developing reagent to use in addition to water a mutual solvent for it and the azide dye salt. Among useful solvents are acetone, ethanol, methanol, dimethylsulfoxide, etc. Alternatively, if the receiving sheet is coated with a film comprising a material having a high electric dipole moment, this surface comprises a third type of highly ionizing environment. The associated azide dye salts of this invention dissociate immediately upon contact with a surface of this type, thus giving a highly colored cation directly. A recording fluid or a transfer sheet employing associated azide dye salts can therefore be used in conjunction with a specially coated paper having a high permanent electric dipole moment to provide novel recording systems.

Exemplary of the recording fluids of this invention is a recording fluid comprising a solution of Michlers hydrol azide (4,4-bis(dimethylamino)benzhydryl azide) in didecyl phthalate, which solution can be used to saturate a stamp pad. When such a recording fluid is transferred by means of a stamp to a web coated with a material having a high permanent electric dipole moment, the indicia imparted thereto become colored immediately. Alternatively, the stamp can be used to transfer the'recording fluid to an absorbent sheet of paper, in which case the color of the imparted indicia is developed by gently heating the paper.

By way of further illustration, recording systems of this invention can be prepared employing ethyl hydrol azide (4,4' bis(diethylamino)benzhydryl azide) or an equivalent colorless dye s'alt of the type described above. In a recording system of this type, such as carbon paper, the associated dye salt is dispersed in a heavy oil or wax-oil mixture and applied to a master sheet. Typewriter type, or a stylus, when pressed against the surface of this master sheet will cause some of the associated dye salt to be transferred to a receiving sheet. If the receiving sheet has an ionizing surface, an immediate color will develop comprising the colored cation of the dye. If an ordinary sheet is used, the color can be developed by means of a developing fluid or by heat as previously described.

The surfaces whose use is indicated in conjunction with the associated dye salt of this invention are those which, as previously stated, bear a high permanent electric dipole moment. Numerous examples of this type of surface are known to the art. Unfired silicates are particularly useful in this regard. Examples of suitable ionizing surfaces are those prepared from unfired silicates such as kaolin, bentonite, activated silica, and the like. Papers hearing such a coating can be manufactured by methods Well known to the art.

The recording fluids and recording systems of this invention will not ordinarily stain skin or fabrics until the final stage of their use when the color is developed in situ on an ionizing surface or by the use of developing chemicals or by heat. In addition, carbon and other copy papers and master sheets prepared from the associated azide dye salts of this invention are either colorless or very lightly colored. Thus, the recording fluids and recording systems provided by this invention are especially advantageous when compared with those commonly employed. Furthermore, since the surfaces of most fabrics are not highly ionizing for the associated azide dye salts of the present invention, the recording fluids employed by this invention are nonstaining and therefore are particularly useful for the printing of price tags or quality control tags on bolts of goods, dresses, clothing, and the like.

An example of a recording solution containing a colorless associated azide dye salt is a 2% solution of Michlers hydrol azide in dioctyl phthalate. This gives an intense blue color on an unfired kaolin-coated receiving sheet.

Another example .of this invention is a 2% solution of ethyl hydrol azide in parafiin oil. This gives an intense blue coloration on an unfired-diatomaceous earth-coated paper.

Another example of this invention is a 2.5% solution of dinitro crystal violet azide in xylene. This gives an immediate blue-black coloration on an unfimd kaolincoated receiving sheet.

Another example of this invention is a 2.5% solution of mononitro crystal violet azide in toluene. This gives a deep violet coloration on an unfired kaolin-coated receiving sheet.

Still another example of this invention is a 3% solution of p-methoxy-p'-dimethylarninobenzhydryl azide in dioctyl phthalate. This gives a wine-red color upon contact with an activated silica-coated paper. This color has very poor light-stability.

Still another example of this invention is a 2.5 solution of 2,2-dichloro-4,4'-bis(dimethylamino)benzhydryl azide in a mixture of 75% paraifin oil-25% dioctyl phthalate by weight. This gives an intense blue color on an unfired bentonite-coated receiving sheet.

Similar recording fluids can be prepared by substituting other azide salts of 'diarylmethane and tri-arylmethane dyes falling withinthe scope of this invention in the above nonionizing solvents or their equivalents. These recording fluids will yield colored indicia upon contact with a highly ionizing surface or, if printed upon a plain surface, the color can be developed by contacting the surface with an ionizing reagent such as aqueous alcohol or simply by applying heat to the surface.

It should be clearly understood that the invention is not limited to the examples set forth but is generally applicable to any associated dye salt containing an azide anion which is water-insoluble and which can be ionized to a colored cation by application of heat or by contact with highly ionizing liquids or solids.

It is also to be understood that the associated azide dye salts of this invention may be used to make recordings on appropriate surfaces by any desired or conventional method or technique. For instance, the salt dissolved in a solvent may be used for direct printing on appropriately coated paper or the salt may be utilized as a component of the coating of a transfer sheet. In other words, the recording media of this invention may be used in a great variety of recording, printing, and 'manifolding systems.

Having described my invention, I claim:

1. The method of printing which comprises applying to an unfired silicate surface characterized by high ionizing power a substantially colorless associated salt of an arylmethane dye base characterized by a logarithmic dissociation constant below 7 and hydrazoic acid whereby physical contact of the associated compound and the silicate dissociates the compound to the intensely colored cation of the dye and produces color on the silicate surface.

2. The method of printing which comprises applying to a surface characterized by high ionizing power a substantially colorless associated salt of an arylmethane dye base characterized by a logarithmic dissociation constant below 7 and hydrazoic acid whereby physical contact of the associated compound and the ionizing surface dissociates the compound to the intensely colored cation of the dye and produces color on the ionizing surface.

3. The method of printing which comprises applying to a surface characterized by high ionizing power a substantially colorless liquid, said liquid comprising a substantially colorless associated salt wherein the anion is an azide ion and the cation is a colored dye cation of an arylmethane dye base characterized by a logarithmic dissociation constant below 7, whereby physical contact of the colorless associated compound and the ionizing surface dissociates the compound to the intensely colored cation of the dye and produces color on the ionizing surface.

4. The method of claim 3 wherein the colored dye cation is an N,N-alkylated-4,4-diaminobenzhydryl cation.

5. The method of claim 3 wherein the colored dye cation is a triarylmethane dye cation.

6. The method of printing which comprises applying to a surface having thereon a coating comprising an unfired silicate characterized by high ionizing power a substantially colorless liquid which comprises an oil-soluble, Water-insoluble salt wherein the anion is an azide anion and the cation is a colored dye cation of an arylmethane dye base characterized by a logarithmic dissociation constant below 7, whereby physical contact of the colorless associated salt and the ionizing silicate dissociates the salt to the colored cation of the dye to provide a colored print.

7. A recording fluid comprising a solution in a nonaqueous solvent of an associated arylmethane dye salt wherein the anion is an azide anion and the cation is the intensely colored cation of an arylmethane dye base characterized by a logarithmic dissociation constant below 7.

8. A recording fluid comprising a solution in a nonaqueous solvent of an associated dye salt wherein the anion is an azide anion and the cation is an N,N-alkylsited-4,4-diaminobenzhydryl cation.

9. A recording fluid comprising a solution in a nonaqueous solvent of an associated dye salt wherein the anion is an azide anion and the cation is the intensely colored cation of dinitro crystal violet base.

10. A new composition of matter comprising the associated dye salt wherein the anion is an azi'de anion and the cation is the intensely colored cation of dinitro crystal violet base.

11. A new composition of matter comprising the associated dye salt wherein the cation is an N,N-alkylated- 4,4'-diaminobenzhydryl cation and the anion is the azicle anion.

12. A new composition of matter comprising the associated dye salt of hydrazoic acid and 4,4-bis(dimethylamino)benzhydrol.

References Cited UNITED STATES PATENTS MURRAY KATZ, Primary Examiner. 

1. THE METHOD OF PRINTING WHICH COMPRISES APPLYING TO AN UNFIRED SILICATE SURFACE CHARACTERIZED BY HIGH IONIZING POWER A SUBSTANTIALLY COLORLESS ASSOCIATED SALT OF AN ARYLMETHANE DYE BASE CHARACTERIZED BY A LOGARITHMIC DISSOCIATION CONSTANT BELOW 7 AND HYDRAZOIC ACID WHEREBY PHYSICAL CONTACT OF THE ASSOCIATED COMPOUND AND THE SILICATE DISSOCIATES THE COMPOUND TO THE INTENSELY COLORED CATION OF THE DYE AND PRODUCES COLOR ON THE SILICATE SURFACE. 